ext4: fix fencepost error in lazytime optimization

Commit 8f4d8558391: "ext4: fix lazytime optimization" was not a
complete fix.  In the case where the inode number is a multiple of 16,
and we could still end up updating an inode with dirty timestamps
written to the wrong inode on disk.  Oops.

This can be easily reproduced by using generic/005 with a file system
with metadata_csum and lazytime enabled.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e057c6fcc227c200a044c8406c7a6023c522f2bf..4ad73d3c100330e7bebaa304431ce2609cde83c0 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4348,7 +4348,12 @@ static void ext4_update_other_inodes_time(struct super_block *sb,
        int inode_size = EXT4_INODE_SIZE(sb);
 
        oi.orig_ino = orig_ino;
-       ino = (orig_ino & ~(inodes_per_block - 1)) + 1;
+       /*
+        * Calculate the first inode in the inode table block.  Inode
+        * numbers are one-based.  That is, the first inode in a block
+        * (assuming 4k blocks and 256 byte inodes) is (n*16 + 1).
+        */
+       ino = ((orig_ino - 1) & ~(inodes_per_block - 1)) + 1;
        for (i = 0; i < inodes_per_block; i++, ino++, buf += inode_size) {
                if (ino == orig_ino)
                        continue;